Lifetime prediction methods for p-MOSFET's: a comparative study of standard and charge-pumping lifetime criteria

Abstract : Lifetime prediction methods are compared for buried-channel p-MOSFET's DC-stressed under hot-electron injections. Experiments are achieved with current-voltage and charge-pumping measurements in order to find a reliable lifetime evaluation with regard to the time-dependent degradation. It is shown that a large difference appears whether one considers a logarithmic or a power time-dependent law for the degradation of the maximum of the transconductance. This arises from the difficulty to extrapolate to the working voltage when the gradients vary with time. We used a modified charge-pumping technique in order to compare the hot-carrier immunity of different drain structures. The local increase in the negative trapped charge is compared to the degradation of the threshold-voltage shift, the relative changes of the drain current, and of the transconductance. A close correlation is found between the transconductance degradation and the oxide charge in conventional p-devices where the degradation is dominated by the channel shortening. In deep-submicrometer LDD p-devices, the increase in oxide charge and interface traps in the graded-drain region plays a significant role in the change in the channel shortening and series resistance. The local build-up of the oxide charge is shown to grow logarithmically in time. Comparisons of a lifetime prediction method based on the trapping phenomena with I-V lifetime criteria show that the maximum of the transconductance degradation is better correlated to the oxide charge than the other parameters.